Hello again everyone! In this instructable I will be showing you how to build a 79cc, 4 stroke motorized bicycle from scratch (not a kit motor). The bicycle we will be building is far superior to kit motors in pretty much all areas, including speed (minimum 35 mph, and that's if you gear it for hills), gas mileage (100+ mpg), noise level (much quieter than a 2 stroke), pollution (meets EPA emission standards), and reliability. Let's get started!

PS: sorry for the crappy quality video, I'll upload a better one at some point once I figure out how to do editing and stuff.

Step 1: Part 0: Laws

Before you begin, it is a good idea to check the laws in your state or country, as motorized bicycles are not legal everywhere. Here are a few links to help you out:




Thanks a lot
Wonderful work<br>Hi i was wondering what you think of the 79cc monster 80 kit available from gasbike.net for 200$ i was thinking about it it sounds a lot more economical than the albeit better but far more expensive one you articulate thanks please advise
<p>That kit is trash. First off, it doesn't include all the parts you'll need to build it. Secondly, many of the parts it does include are either crappy, or very unlikely to work. For example the gas tank and exhaust will not fit in pretty much any bike frame, plus the gas tank is ugly and small, and the exhaust is rather restrictive and loud, and the jackshaft gear ratio is wrong. Also the sprocket they provide is way too thin and of very low quality, and the sprocket adapter will rip the spokes out of your wheel. The mounting hardware is also of questionable quality. So basically you'd be paying $200 plus shipping for the engine block and a couple of chains. You'd have to spend at least another $400 to get to the point where you'd have a bike that you could actually ride, and that's if you can make your own exhaust pipe. If you aren't good at TIG or Oxy-Acetylene welding, add another $80 or so. Long story short, you'd be wasting your money buying a kit. However, if you check craigslist frequently and find a good deal on a bike, you could do a build which works perfectly find for about $700-800 or so, including the cost of the bike. It wouldn't be as nice as the red bike, probably have no front suspension, no mag wheels, and a cheaper disc brake, or caliper or V brakes, but it would be functional, and you could always upgrade later.</p>
Here is a link for a quick look<br>https://www.gasbike.net/collections/engine-kits/products/79cc-monster-80-bike-engine-kit-4-stroke
Link me to the exhuast couldnt find one
<p>There used to be 2 pipes that would work on affordablegokarts.com, however I'm no longer seeing them. I'll do some digging, and if I can't find one, I could make you one or tell you how to make one if you've got a friend who has a TIG or acetylene welder.</p>
<p>I contacted AGK, and apparently they no longer carry the premade exhaust pipes for the 79cc predator engine. I'll update the instructable within a few weeks, going through the process of making your own exhaust pipe, if you don't have access to a TIG or acetylene welder or find that it's too expensive to have a welding shop do it, PM me and I'll see about making one for you.</p>
<p>Thanks for the info</p>
<p>Here are a few pictures of the parts I have accumulated. What kind of reduction gear/transmission would you suggest I get to keep the rear spokes in tact?</p>
<p>Sorry to break it to you, but you got a pretty bad bike to motorize. I'd return it if you still have the receipt and instead look for an old mountain bike on craigslist. If you do use it, you'll need to replace the rear wheel, there's no way to attach a sprocket to it, and the springer fork, which is super flimsy, and add some brakes. A rear coaster brake as your only brake is going to get you killed. When you replace the springer fork you should get one with disc brake mounting tabs and add a nice front disc brake. Buy (or build) a jackshaft such as the ones shown in the instructable. GTC Manufacturing sells one for a go-kart that will work if you swap out the gears. Alternatively you can build one with steel plates and pillow block bearings.</p><p>As for the other stuff, you still need a lot of parts. Air filter, exhaust pipe, throttle, throttle linkage, lots of other stuff, etc.</p><p>You also have a hub adapter, which means that mag wheels are unfortunately out unless you want to buy another adapter. Although buying mag wheels and an adapter might be cheaper than getting a custom built spoked wheel strong enough to hold up to the motor. You can get a set of super sturdy mag wheels with disc brake mounts for about $250 from mbrebel.com or you can search &quot;teny rims&quot; on ebay and get some of those. Just make sure they are disc brake compatible, cause hub adapters don't work on mag wheels unless you have access to a machine shop and can make your own. I've made my own disc adapters, but hub adapters are harder.</p><p>Have you removed the governor system yet?</p><p>Also do you know what RPM your clutch engages at? If it's more than about 3,000 or less than 2,200, you'll have issues.</p><p>I'd recommend carefully re-reading all of the instructable and gaining a thorough understanding of what you're trying to build before you buy anything else.</p>
<p>I have a HF 79 cc gas engine and a new bicycle and all the stuff needed to put a motorized bike together...except a transmission. I have a heavy duty centrifugal clutch and the rear sproket. Do I need a transmission?</p>
<p>Also, post some pics! Even if it's just the parts you have so far, I can probably make some recommendations. </p>
<p>If by transmission you mean a jackshaft for 2 stage gear reduction, then yes, you need a transmission. Unless you can fit like a 150 tooth rear sprocket, but that would be impractical, very expensive, and look ridiculous. Having a jackshaft will also help you to get proper sprocket alignment.</p>
I need more teeth somewhere for better acceleration. SO which sprocket on the jackshaft should I change? Or should it be the rear sprocket?<br>
<p>Yea, I figured if it went over 40 you might be a little lacking in acceleration. I find that for a rider like me who weighs about 155 pounds, a 13:1 gear ratio is pretty good if you're running 26&quot; tires. What are the tooth counts on your current sprockets? Also what's up with the top bar of your frame? Did you cut it out and re-weld it to fit the engine?</p>
<p>The clutch=11T</p><p>Sprocket = 22T and 9T</p><p>Rear sprocket = 42T</p><p>And yes, I cut the top bar. But I have not welded a modified bar in place yet. But I plan on doing it before &quot;riding season&quot; begins again. I might even get a new bike for this build like this one: <a href="http://www.bikebuyers.com/fito_marina_alloy_1sp_man_black.htm?gclid=Cj0KEQiAk5zEBRD9lfno2dek0tsBEiQAWVKyuGmx3yhesxPD4HnLf5wcLYZcseYMQFvn58fYU0bZI7kaApko8P8HAQ" rel="nofollow">http://www.bikebuyers.com/fito_marina_alloy_1sp_ma...</a></p>
<p>Yea, right now your ratio is about 9.33:1, way too steep. Try a 30t or 32t in place of the 22t. Also that bike is really unsafe without a top bar. I would not ride it. You should get a new bike frame. The bike you linked to will most likely not fit a predator engine. Look for an old 21&quot; steel frame mountain bike on craigslist, such as a trek 820. If you're having issues finding a large enough frame, some people have done vertical mounted predator engines, which will save some space, but will probably require you to get wide cranks.</p>
<p>Here is the fito marina bike with a 79cc engine: <iframe allowfullscreen="" frameborder="0" height="281" src="//www.youtube.com/embed/BMTpUWPbv50" width="500"></iframe></p><p>I have wide cranks. But this bike does not seem to need them. A steel frame would be better, but I don't think I will have to modify this one. I've been looking for a used cruiser, but most cost way more than this bike. Still looking though.</p>
<p>That bike appears to have wide cranks. You really want a steel frame, most aluminum frames do not last long with such a powerful engine. I found my red bike on craigslist for $150. I could have motorized it as-is and it would have turned out ok. However I upgraded just about everything on it, so it cost me a lot more. Front suspension is really nice to have though.</p>
<p>So is anyone attempting to build one of these yet?</p>
<p>I built one. But not exactly like this one.</p>
<p>Cool. How fast does it go?</p>
<p>I have only had it up to 40mph but it will go faster.</p>
<p>How's the acceleration?</p>
I'd love to see a picture!
<p>great work!</p>
<p>Man, amazing write up, I am so tempted to try this... but TBH thinking I should maybe do an easier kit (or something closer to a kit build) my first go at motorizing a bicycle.</p><p>Any recommendations on something a bit easier to get my feet wet... been thinking about maybe starting with a Grubee Aluminum frame (not sure on GTA or GTS yet). I definitely wanna build something with enough power to have some fun, but I'm only 160lbs and traveling on mostly flat land (tho there are some decent hills I'd also like to be able to do)... and would like to at least hit a solid 35mph, 40 would be nice. Is a kit a bad idea, where I should just get the parts separate? or are there some decent kits to get starting. I have an electrical engineering degree, and am good with my hands, but by no means an export on motors. Also don't mind spending in the 1k range (more if necessary) for my first go, tho I have a feeling I'll be building a second one very shortly after. Think the Grubee frame would be a good start? any recommendations on what to put on one? I'm hoping to build something like this on maybe my 3rd go (maybe my second if I get balsy), so think 2 steps down from the build you describe here.</p>
<p>Glad to see someone who might actually be interested in building one! </p><p>So, first off, on the frame, it's an aluminum frame, which I don't like. Aluminum fatigues much faster than steel, leading to a broken frame rather quickly. The blue road bike that is in one of the intro pictures had an aluminum frame, which broke within a thousand miles. Also, if you buy a bare-bones frame with nothing else on it, expect to spend a LOT more on parts than if you just bought a craigslist bike and swapped out parts, especially if you need to have the shop build the bike for you.</p><p>Second, on kit engines: I find that the Chinese 2 stroke kits are made as cheaply as possible, and contain many inferior parts that will require immediate replacing to get the bike running, and many more that will need to be replaced if you want to go more than 25 mph. For example, the stock sprocket that comes with the chinagirl engines attaches to your wheel by clamping onto the spokes. Not only does this provide no way of properly aligning the sprocket, but it will also quickly rip the spokes out of your wheel and pull it out of true. If you know a lot about 2 stroke engines, enjoy tinkering, and aren't looking for a reliable mode of transportation, but just something to have fun with, go ahead and get a 2 stroke kit for the first build. But know that if you want to hit anywhere near 35 or 40 mph, you will need to do a TON of engine modifications. I'm talking porting the engine, replacing and tuning the carb, welding your own exhaust pipe, and a bunch of other things. Also, unless you have a heavily modified and upgraded 2 stroke, you will have to choose between speed or hill climbing power. The engines simply aren't powerful enough to give you both.</p><p>On my bikes: It looks harder than it is. Unlike the 2 stroke kits, the predator engines will start right out of the box, without any carb tuning or part replacement. The magneto will not die instantly if you get a bit of water on it. The spark plug boot and fuel line will not disintegrate in the sun. And, perhaps most importantly, I have provided you with extremely detailed instructions on how to build one. Also hitting 40 and still being able to climb most hills is easily within the grasp of the 79cc predator engine.</p><p>Whatever you choose to build, I'd be happy to help you build it by answering questions, giving advice, and troubleshooting.</p><p>The blue bike was my second build btw. My first was a 66cc 2 stroke kit. Black was my third, Red was the 4th.</p><p>BTW, if you're wondering what would be a step <em>up</em> from the predator bikes... <a>This</a> is what I'm currently building. </p>
<p>Thanks for the quick response. I'm now thinking about going with a Golden Eagle kit to get me started (they seem a little pricey, but also reliable and easy to build on a wide range of bikes)... then giving this a shot for my second build (I'm just worried about the time and space right now... I am renting, and while my landlord has a TON of tools and would help, sadly he's more into wood work than metal... I don't have a workspace I could take up for a week, let alone a few right now.</p><p>What I am wondering is, if it would be possible, and if so how hard it would be, if I got the golden eagle mount kit (https://www.bikeengines.com/shop/mount-kit-only-without-the-engine-36-spoke-2/) and tried to attach the 79cc predator to it. I feel like that would be the ideal situation for my first build, with more than enough power... and would get my feet wet enough that this build would likely not seem too hard after doing.</p>
<p>The golden eagle mount kit might be fine for smaller engines, but it looks a little flimsy to hold up to a larger engine. Also you would probably have to modify it a lot to get it to accept a predator engine, enough that it would probably be more work than just making one from scratch. Also $375 is a lot of money for just a mounting kit. You could buy all the metal and tools you'd need to build one from scratch for less. You can really get away with using only a drill and a handheld angle grinder with cutoff discs for mount fabrication, it won't look nice, but it will function fine. Also you can build the engine mount in a day easily, it takes me about 3 hours to put together an engine mount.</p><p>Another thing I notice about the golden eagle mounting kit is that it has a belt drive which attaches to the spokes. While this may be fine for sturdy wheels paired with a really small engine, the predator is powerful enough to rip the spokes out within the first 100 miles. Remember we are talking about an engine that is easily 4 times more powerful than any of the golden eagle engines. Also doing a rear mount for a larger engine is going to significantly raise your center of gravity and make it a lot easier to lose control.</p><p>Another thing is that using the golden eagle kit, I have no idea what gear ratio the kit has, it might be completely wrong for a predator engine.</p><p>Also IMO golden eagle is really overpriced, for the cost of some of their engines I could build a decent predator bike if I got lucky on craigslist; although there are some who swear by them as well. Make of that what you will.</p>
<p>OK, you clearly have some very good points, thank you for the long response. Starting to seriously consider this build... wish I had a workbench I could use for a week, but my current renting situation won't allow that. But I think if I break this into a few different days of work, I should be able to manage. I'm hoping I'm not jumping in too deep on this one, still debating on maybe building a smaller 4 stroke setup first... but you are completely correct about the GEBE kit being pretty damn overpriced. I figure building the engine mount and bracket and getting it on the bike is going to be the hardest part (I hope)... tho also hoping the engine modifications are easy enough, your instructions seem clear enough, but I am no expert on engines. I'm thinking about picking up the engine at Harbor freight tomorrow, even if I end up building another kit first, would be good motivation to get this thing going (and thinking it probably makes sense to just build what I want the first time).</p><p>I suppose the big step now is finding the right bike. There's a ton of used bikes here in the SF Bay Area luckily, but still seeing something that looks like it'll be a good fit (at least not getting any response from people with anything that looks good). But I will keep looking.</p><p>Thanks again for all the info, hoping I can piece most of the parts this week, and start figuring out how I want to break up the work and tackle this.</p>
<p>I'm sending you a pm with my email.</p>
<p>BTW, your 'this' link is not a real link.</p>
<p>wow! You have a gift! Think engineering! I also hope to see you in the 2020 Tokyo Olympics in archery!</p>
<p>Love the idea and your detailed solutions to the design and engineering (first class 'ible as well) but is the braking up to the job. <br><br>The energy to dissipate in braking is dependent upon mass and velocity squared. You will be much heavier and going much faster than a pedal bike. Perhaps the brakes from a small motorcycle and also uprated forks so they don't fold or snap in an emergency stop... and tyres with a bit more rubber contact for the road. Be safe.<br></p>
<p>The brakes are more than adequate, I made sure of that. I have a top of the line front disc brake with a 200mm rotor, which provides a rather ridiculous amount of stopping power, as well as a good caliper brake on the rear, and when you let off the throttle, the engine acts as a secondary brake at speeds of over about 10 mph due to the clutch engaging when spinning in either direction.</p>
<p>Great, This is a deluxe cuban Rikimbili ...</p><p>http://www.rikimbili.com/</p>
<p>Yea, that's where I got the original idea to build one of these, my dad leads photography tours in cuba every few years and once told me that motorized bicycles were everywhere, that got me thinking...</p>
<p>it's great dude. In my country, this is becoming a great stuff, a bicycle with machine. </p>
<p>This is cool! I'm 68 years old, halfway chair-bound but still a woodworker. I'm always telling grandma that if you want to know something then go ask a teenager. Riding along with you this morning made me smile right here in my pillow-stuffed chair. Iforgabout the pain in </p>
<p>From now on, please no comments about such and such being illegal or whatever. I have added a &quot;check your local laws&quot; step. Any future comments ranting and raving about legality will be flagged for deletion.</p>
<p>This looks awesome. Unfortunately in Germany this is a no-go. Any motor in a bike will make it a motorbike (hence the word). Which means you need a license. Which needs approval for public traffic. Which will cost you about the same you spent for the expensive version - with low chances you get the approval at all. So this one would only be legal on private property. And we (I mean the majority) do not have ranch-sized estates here.</p>
<p>Fantastic! An absolute Favorite for all time!!!</p><p>I intend to attempt to follow your Instructable as soon as I am able to!</p><p>Thanks alot!!!</p>
<p>First off, good luck and if you have any questions, I'm happy to answer them. Second, you somehow managed to triple post...</p>
<p>how much did you spend on this whole project? Please mention in US dollars.</p>
<p>Can't believe I forgot to include this in the instructable, thanks for catching that. If you get a craigslist bike for $150 and just replace the rear wheel and use the rest as-is, you can probably get away with spending around $1000 or so, maybe a bit less. However, if you build one like the red bike, expect to spend anywhere from $1500-2000.</p>
<p>I have done a couple using a two stroke Ebay kit.</p><p><br><br><br>That fuel tank looks suspiciously Ebay.<br><br><br><br>In Australia anything with an internal combustion engine is regarded as a Motorbike,<br><br>It has to be registered and insured.<br><br><br><br>The Fuzz strike hard, a number of the locals have been fined large sums of money for riding an unregistered vehicle without a proper license.<br><br><br><br>An electrically powered bike of less than 200watts, last time I looked was okay.<br><br><br><br>Batteries are expensive, heavy and run out of electricity<br><br><br><br>To get round this I have built a couple using a MG ( motor generator) set<br><br><br><br>The first used a Whipper Snipper motor direct coupled to a car heater fan acting as a DC generator.<br><br><br><br>This drove another heater fan with a rubber roller on its shaft driving the bicycle rear wheel.<br><br><br><br>This ran quite well though you had to pedal up hill to help it out.<br><br><br><br>I had used hot glue gun glue on the MG set, which melted, Bugger I had to ride home.<br><br><br><br>...........................................................<br><br><br><br>MG sets are heavy so the obvious solution was a &quot;Power Car&quot;<br><br><br><br>The Europeans use bicycle trailers to carry small children groceries etc, they are pretty cheap.<br><br><br><br>With a power car you can use a proper 240v (110v?) generator set.<br><br><br><br>Bicycle wheels with hub motors are readily available on Ebay.<br><br><br><br>You can buy a 200 watt version and be legal ( Australia) or a 1000 watt version <br><br>and try and lie your way out of it if stopped.<br><br><br><br><br><br>The input voltage varies between 24 and 48 v DC<br><br><br><br>You can buy inverters of Ebay that will convert 240v AC to 48v DC just make sure the wattage rating matches the motor.<br><br><br><br>...........................................................................<br><br><br><br>As a further alternative stick with the gen set voltage but use a power tool with roller<br><br>to drive the bicycle wheel.<br><br><br><br>A drill works okay, if you try to use a grinder ( the shape is better) you will probably find it is turning too fast , all you get is blue smoke off the wheel.</p><p><br><br><br><br><br><br><br><br><br><br><br><br><br></p>

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